Imaging of biological tissues and organs assists doctors in both diagnosis and treatment. A variety of medical techniques which are suitable for imaging biological tissues and organs are known. These include traditional x-rays, ultra-sound, as well as magnetic resonance imaging (MRI), and computerized tomography (CT). A variety of dyes used in medical imaging have also been described including radio opaque dyes, fluorescent, as well, as colorimetric dyes (see e.g., U.S. Pat. Nos. 5,699,798; 5,279,298; 6,351,663; and U.S. patent application Ser. No. 10/365,028). Imaging techniques and systems using fluorescent dyes have been described for the heart and eye (see, U.S. Pat. Nos. 5,279,298 and 6,915,154; and U.S. patent application Ser. No. 10/619,548, all of which are incorporated by reference in their entirety). Some dyes can serve both an imaging function, as well as a therapeutic function (see, e.g. U.S. Pat. No. 6,840,933). It would be useful to provide imaging methods and systems that could be used to view vasculature maladies associated with the central nervous system and/or brain.
One example of a malady affecting the brain is cerebral arteriovenous malformation (AVM). AVM is a disorder of the blood vessels in the brain, in which there is an abnormal connection between the arteries and the veins. Thus, a connection between arteries and veins occurs without having the normal capillary bed between them. Arteriovenous malformations vary in their size and location within the brain. It is a congenital disorder. The AVM consists of blood vessels termed “nidus” (nest) through which arteries connect directly to veins, instead of through the elaborate collection of capillaries. Over time, the AVM tends to enlarge as the great pressure of the arterial vessels can not be handled by the veins that drain out of it. This causes a large collection of worm-like vessels to develop (malform) into a mass capable of bleeding at some future time. These malformations are most likely to bleed between the ages of 10-55.
There are often no symptoms until complications occur, which involve rupture of the AVM and a resulting sudden bleed in the brain i.e. a hemorrhagic stroke. When symptoms do occur before an AVM ruptures, they are related to smaller and slower bleeding from the abnormal vessels, which are often fragile because their structure is abnormal.
In more than half of patients with AVM, hemorrhage from the malformation is the first symptom. Depending on the location and the severity of the bleed, the hemorrhage can be profoundly disabling or fatal. The risk of bleeding from an AVM is approximately 2-4% per year. Cerebral arteriovenous malformations occur in approximately 3 out of 10,000 people. If an AVM bleeds once, the risk is greater that it will bleed again in the future. Intracerebral or subarachnoid hemorrhages are the most common first symptoms of cerebral arteriovenous malformation (see, e.g., Ojemann R G, Ogilvy C S, Heros R C, Crowell R M, eds. Surgical Management of Cerebrovascular Disease, Third edition, 2005, Williams & Wilkins, Baltimore).
The first symptoms often include headache, seizure, or other sudden neurological problems, such as vision problems, weakness, inability to move a limb or a side of the body, lack of sensation in part of the body, or abnormal sensations.
Open brain surgery, endovascular treatment, and radiosurgery are some of the treatments used. Often these treatment options will be used in combination. Very large AVMs may short-circuit blood flow enough to cause cardiac decompensation in which the heart is unable to pump enough blood to compensate for bleeding in the brain. This condition is usually identified in infants and young children.
Surgery is dependent upon the accessibility and size of the lesion and the status of the patient at the time of surgery. Open brain surgery is the actual removal of the malformation in the brain through an opening made in the skull.
Systems and methods which provide for imaging vasculature associated with AVM would assist the surgeon in locating the AVM and thus would aid in achieving a successful outcome to the procedure. Similarly, the same methods and systems could be used to confirm that the AVM has been removed.
Traditional imaging methods used in the context of AVM, such as measuring arterial pulsation or angiography using digital subtraction are either unreliable or expensive and inconvenient to be used during surgery (see, e.g., Wrobel et al., 1994, Neurosurgery 35(5):970; Martin et al., 1990, J. Neurosurg. 73:526). A need therefore exists for improved imaging methods and systems which provide for the rapid, accurate and inexpensive imaging of maladies affecting the vasculature associated with the brain and central nervous system, e.g., AVM.